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Coil tapping humbuckers



Coil taps are an extremely simple way of producing a fundamental character change in the tone of a guitar, both from the point of view of function and operation, and installation. The apparent extra treble is generally enhanced by the use of 1n0 capacitors on backed off volume controls, giving a breathy, edgy sound that goes some way towards a Telecaster's character, though other physical changes are necessary to help overcome the difference between the Tele's taut 25½ inch scale and the 24¾ inch scale found on most guitars fitted with humbuckers. But, physical stuff aside, coil taps are pretty much the bee's knees in simple modifications. Volume drop can be a nuisance, and where it is not possible to overcome this by using floor volume pedals or compressors, a partial tap can help.

Figure 1

Turning one coil off altogether can be done by leaving it open circuit or without earth reference, or by earthing one of the pair out partially or completely. Earth-type taps are the simplest to add, as the extra wire does not require screening. The extra wire is added to the join between the coils as in Figure 1. Here, earthing the tap wire will cut out coil 2. Switching can be done by an on/off switch, or preferably for cosmetic reasons, by a mini-toggle SPDT (single pole, double throw). The mini-toggle switches are generally available with a ¼" shaft, and as the external appearance is similar with a variety of S/DPDT's, it will tie in with other modifications such as phase or series/parallel — of which more at a later stage. It is unwise to use a push button latching action switch, as you will have no visual check on mode, whereas with a mini-toggle, you can see which way the thing is set before you start.

To wire an on/off SPDT, run the tap wire to the centre terminal, and wire from one of the outer terminals to earth, as in Figure 2.

Figure 2

The alternative partial tap, which avoids a big volume drop, runs to earth via a capacitor, and this will take out the treble frequencies of coil 2, leaving the bass end of the pick-up humbucking, and allowing the treble frequencies of coil 1 to dominate the tone. This gives a weightier sound than a complete tap, and in my experience, requires a harmonically rich pick-up for best results — I would use it on a power pick-up rather than a vintage type. To wire it, simply replace the earth wire from terminal 3 with a capacitor. It is worth experimenting with different value capacitors to get the results most suited to you and your guitar. I use 33nF on my regular guitar; Lawrence recommend 20nF for their pick-ups, and I would suggest you experiment with capacitors between 10 and 50nF. Much will also depend on pick-up position, and capacitors are cheap enough anyway. Voltage rating is irrelevant except in that higher voltage units will be more robust and will be less susceptible to heat damage.

Capacitor value has another bearing on the sound in that the deeper down the frequency range that it cuts, the deeper will be the hum. That is, the pick-up will still be humbucking below the level that the capacitor removes to from one coil — the hum from a 10nf tap will be shallower than the hum from a 50nF tap, and complete tap will have all the hum that the humbucker usually cancels out.

Figure 3

I have found it useful on several custom guitars to be able to alternate between complete and partial tap and this can be done by using an on/off/on SPDT as in Figure 3. The three switch positions give partial tap/humbucker/complete tap, and here, you may even find it useful to vary between different value partial taps rather than partial and complete. You could try, for example, a 10nF capacitor from terminal 1 to earth and a 50nF from terminal 3 to earth. It has often been said that differences between capacitor values on tone controls are hard to hear, and it could be said that variance between two values on a partial tap are over fussy. However, I have found that seemingly minute changes in tone can make the difference between a satisfying gig and a gig that didn't quite cut it, and that's the best reason for experimenting.



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Lowrey MX-1 Instrument Review

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Organ Talk


Electronics & Music Maker - Copyright: Music Maker Publications (UK), Future Publishing.

 

Electronics & Music Maker - May 1981

Feature by Adrian Legg

Previous article in this issue:

> Lowrey MX-1 Instrument Revie...

Next article in this issue:

> Organ Talk


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